Such a device is known for German Patent Specification 3,000,218, which corresponds to U.S. Pat. No. 4,464,169. Such body cavities are, above all, cavities in the body of humans and animals, especially the abdominal cavity. But body cavities are also regions which are not cavities per se, such as the gap in the knee joint which can be widened to form a body cavity by pumping it up.
Devices of the known type require a large number of components and measuring element. Moreover, in all the instruments, the measurement of the pressure in the body cavity is carried out in such a way that the gas through-flow is reduced to zero. The maximum obtainable throughflow is thus restricted considerably. Furthermore, the gas throughflow has an appreciable pulsation.